1. Technical Field
This application is related to micro-mechanical chemical sensors, and more particularly, to micro-mechanical sensors with chemoselective material layers operated in a dynamic mode.
2. Description of Related Technology
Small, portable, reusable chemical sensors that are both sensitive and selective are desired for applications ranging from remote sensing to counterterrorism to warfighter safety. One sensing technology that has been extensively studied to satisfy these criteria is arrays of sorbent polymer coatings as the sensing element of an “electronic nose”, as described in R. A. McGill, M. H. Abraham, and J. W. Grate, “Choosing polymer-coatings for chemical sensors,” Chemtech 24(9), 27-37 (1994); 2. A. J. Ricco, R. M. Crooks, and G. C. Osbourn, “Surface acoustic wave chemical sensor arrays: New chemically sensitive interfaces combined with novel cluster analysis to detect volatile organic compounds and mixtures,” Acc. Chem. Res. 31, 289-296 (1998); and S. L. Rose-Pehrsson, J. W. Grate, D. S. Ballantine, and P. C. Jurs, “Detection of hazardous vapors including mixtures using pattern-recognition analysis of responses from surface acoustic-wave devices,” Anal. Chem. 60(24), 2801-2811 (1988).
Micromechanical sensors can be classified into two general classes: (i) displacement-sensitive sensors that are operated in a static mode that is far below the device's mechanical resonant frequency; and (ii) resonant sensors that are operated in a dynamic mode at or near the device's mechanical resonance frequency.
Recent research has focused on arrays of ultra-sensitive microcantilevers whose sorption induced bending or resonant frequency change is read-out electronically or optically. See, for example, T. Thundat, E. A. Wachter, S. L. Sharp, and R. Warmack, “Detection of mercury-vapor using resonating microcantilevers,” Appl. Phys. Lett. 66, 1695-1697 (1995) describing microcantilever sensors. N. Abedinov, C. Popov, Z. Yordanov, T. Ivanov, T. Gotszalk, P. Grabiec, W. Kulisch, I. W. Rangelow, D. Filenko, and Y. Shirshov, in “Chemical recognition based on micromachined silicon cantilever array,” J. Vac. Sci. Technol. B. 21(6), 2931-2936 (2003), disclose electronic read-out of microcantilever sensors. L. R. Senesac, P. Dutta, P. G. Datskos, and M. J. Sepaniak, in “Analyte species and concentration identification using differentially functionalized microcantilever arrays and artificial neural networks,” Analytica Chimica Acta 558, 94-101 (2006) disclose optical read-out of microcantilever sensors using time division multiplexing with optical measurement of cantilever deflection.
Recent work has included mass detection at the level of 6 femtograms, as described in N. V. Lavrik and P. G. Datskos, “Femtogram mass detection using photothermally actuated nanomechanical resonators,” Appl. Phys. Lett. 82, 2697-2699 (2003). Chemical vapor detection at a level of 30 parts-per-trillion is described in L. A. Pinnaduwage, V. Boiadjiev, J. E. Hawk, and T. Thundat, “Sensitive detection of plastic explosives with self-assembled monolayer-coated microcantilevers,” Appl. Phys. Lett. 83(7), 1471-1473 (2003).
Detection of single DNA base pairs has been demonstrated, as discussed in J. Fritz, M. K. Baller, H. P. Lang, H. Rothuizen, P. Vettiger, E. Meyer, H.-J. Guntherodt, C. Gerber, and J. K. Gimzewski, “Translating biomolecular recognition into nanomechanics,” Science 288, 316-318 (2000).
Optical read-out approaches in particular have the potential for extremely high sensitivity, as discussed in T. H. Stievater, W. S. Rabinovich, H. S. Newman, R. Mahon, D. McGee, and P. G. Goetz, “Measurement of Thermal-Mechanical Noise in Microelectromechanical Systems,” Appl. Phys. Lett. 81, 1779-1781 (2002). Remote optical interrogation of cantilever sensors is discussed in E. A. Wachter, T. Thundat, P. I. Oden, R. J. Warmack, P. G. Datskos, and S. L. Sharp, “Remote optical detection using microcantilevers,” Rev. Sci. Instrum. 67(10), 3434-3439 (1996).
Optical read-out based on a beam deflection method is described in T. Thundat, E. A. Wachter, S. L. Sharp, and R. Warmack, “Detection of mercury-vapor using resonating microcantilevers,” Appl. Phys. Lett. 66, 1695-1697 (1995) and L. R. Senesac, P. Dutta, P. G. Datskos, and M. J. Sepaniak, “Analyte species and concentration identification using differentially functionalized microcantilever arrays and artificial neural networks,” Analytica Chimica Acta 558, 94-101 (2006). These systems can be difficult to miniaturize and/or package due to the physical separation required between the optical detector and the microcantilever sensor.
A system and method for optical interrogation of MEMs sensors using microcavity interferometry is disclosed in U.S. Patent Publication US2007-0125150A1 (Ser. No. 11/559,119), to Todd H. Stievater, William S Rabinovich, Eric J Houser, Stanley Vincent Stepnowski, and R. Andrew McGill. The entire disclosure of this patent application is incorporated herein by reference. Optical interrogation of MEMS sensor is discussed in T. H. Stievater, W. S. Rabinovich, H. S. Newman, J. L. Ebel, R. Mahon, D. J. McGee, and P. G. Goetz, “Microcavity Interferometry for MEMS Device Characterization,” J. Microelectromech. Syst. 12, 109-116 (2003). Photothermal actuation of a micromechanical system is disclosed T. H. Stievater, W. S. Rabinovich, M. S. Ferraro, N. A. Papanicolaou, J. B. Boos, R. A. McGill, and J. L. Stepnowski, “All-Optical Micromechanical Chemical Sensors,” Appl. Phys. Lett. 89, 091, 125 (2006).
D. W. Can and H. G. Craighead, “Fabrication of nanoelectromechanical systems in single crystal silicon using silicon on insulator substrates and electron beam lithography,” vol. 15, pp. 2760-2763 (AVS, 1997) discloses nano-scale resonators.
A photonic microharp chemical sensor is disclosed in T. H. Stievater, W. S. Rabinovich, M. S. Ferraro, N. A. Papanicolaou, R. Bass, J. B. Boos, J. L. Stepnowski, and R. A. McGill, “Photonic microharp chemical sensors,” Opt. Express, Vol. 16, pp. 2423-2430 (February 2008), the entire disclosure of which is incorporated herein in its entirety.